Radial turbine shroud construction



May 21, 1968 N ET AL 3,384,345

RADIAL TURBINE SHROUD CONSTRUCTION Filed Aug. 15, 1966 2 Sheets-Sheet 1 FIG.

INVENTORS Norman NEATH Allen B. NEWLAND Arthur D. STRELSHIK A TTORNEY May 21, 1968 N. NEATH ET AL 3,384,345

RADIAL TURBINE SHROUD CONSTRUCTION Filed Aug. 15, 1966 2 Sheets-Sheet 3 INVENTORS Norman NEATH Allen B. NEWLAND Arthur D. STRELSHIK ATTORNEY;

United States Patent RADIAL TURBINE SHROUD CONSTRUCTION Norman Neath, Longueuil, Quebec, Allan Burrell Newland, Lambert, Quebec, and Arthur David Strelsliik,

Montreal, Quebec, Canada, assignors to United Aircraft of Canada Limited, Longueuil, Quebec, Canada Filed Aug. 15, 1966, Ser. No. 572,338 14 Claims. (Cl. 253-39) The present invention relates to radial or centripetal turbines, and more particularly, to the construction of the shroud section covering the base of the rotor of such turbines.

Problems arise in the construction of such a shroud section due to the high temperature gradients involved and the necessity for maintaining an eflicient seal against the escape of high pressure gas. The problem is particularly severe in the case of radial turbines which require a shroud section of considerable radial depth. The gas input at the radially outer periphery is at a very high temperature, and a substantial gradient is induced both across the thickness of the shroud annd also radially inwardly towards the hub of the rotor due to cooling of the gas as it passes through the turbine.

The temperature differentials make it desirable to construct the shroud section in a number of different components, both to allow some radial expansion and, if necessary, to allow the use of different materials for the inner and outer components which are subjected to different temperatures and different axial temperature gradients. However, the construction of a shroud in a number of components aggravates the problem of obtaining an efficient seal.

The shroud construction of the present invention overcomes these problems in a relatively simple and ingenious manner as will hereafter become apparent.

In accordance with one form of the invention, there iS provided in a centripetal turbine having:

Stationary framework,

A rotor,

A rotor base,

A shroud including a section spaced from the rotor so as to cover at least the portion of said base exterior to the hub, and support means mounting said section to said framework,

The improvement wherein said shroud section comprises a plurality of separate concentric annular components arranged in mutual abutment to present a substantially continuous surface on the side adjacent said rotor,

Said components having dividing edge areas which overlap in radial and axial directions so that when inner and outer rims of said section are under axial tension, the components are substantially rigidly interlocked and sealed against escape therebetween of high pressure gas from the rotor side, said support means being arranged to maintain such axial tension.

Preferably, the dividing edge areas at the radially outer extremities of the components overlie the dividing edge areas at the radially inner extremities of the next adjacent radially outward component, the inner rim of the section being held by the support means in tension, with respect to the outer rim, in a direction axially away from the rotor.

The components of the shroud section are held in axial tension so as to interlock by means of the support means, which may comprise a cylindrical portion shaped at one end to engage and grip the outer rim of the shroud section, the portion extending in a direction axially away from the rotor to an opposite end which is fixed to part of the stationary framework of the turbine, the support including an annular tapering portion extending from an outer rim rigid with the cylindrical portion at a position spaced from the rotor end, to an inner rim shaped to engage and grip the inner rim of the shroud section, the inner rim of the tapering portion being in its engaged position resiliently displaced axially from its position of equilibrium so as to maintain the necessary axial tension between the inner and outer rims of the section.

By position of equilibrium is meant the position of the rim of the tapering portion which it would normally take up in an unstrained or unstressed condition.

Having thus generally described the invention, an embodiment thereof is more particularly described by way of example and by reference to the accompanying drawings, in which:

FIGURE 1 is an axial section through part of a centripetal gas turbine engine showing the rotor and shroud section at the base of the rotor;

FIGURE 2 is a radial section along the line 22 of FIGURE 1; and

FIGURE 3 is an enlarged view of the inner rim parts of the shroud support means, showing the method of construction which results in the tensioned condition of the shroud components.

In the drawings there is shown a turbine portion including a rotor 10 having a hub 11 and blades 12, a stationary framework generally indicated at 13, a peripheral shroud section 14, and a shroud section 15 covering the base of the rotor in between its hub and outer periphery.

The shroud section 15 is made up of three concentric components, an inner component 15a, a central component 15b, and an outer component 150.

It will be seen that the dividing edge areas of the components 15a, 15b, 150, are stepped so as to overlap in radial and axial directions. Thus, the outer edge of inner component 15a has a radial edge abutting a radial edge of component 15b and also a radial edge area overlying on the rotor side, a radial edge area of component 15b. Similarly, component 15b has a radial edge abutting a radial edge of outer component 15c and also an axial edge area overlying on the rotor side, an axial edge area of component 15c.

The shroud components are retained in position by sup port means which consists of two main components 16 and 17. The portion 16 includes a first sheet of resilient metal having a portion 18 in the form of a cylinder and a portion 19 bent radially inwardly at one end to abut a radial face of shroud component 15c. Overlying the cylindrical portion 18 is a second sheet of resilient metal having a cylindrical portion 20 welded to portion 18 and having a part 21 bent radially inwardly in spaced relation from part 19 so as to overlie a rotor side face of shroud component 150, which face is stepped back in a direction away from the rotor from the radial plane P of the continuous surface presented by the shroud to the rotor. Thus, the outer rim 21 of the shroud section 15 is gripped between parts 21 and 19 of the shroud support.

The portion 17 of the shroud support includes a first sheet of metal having a generally frusto-conical portion 22, an outer cylindrical portion 23 at the outer extremity of the frusto-cone and which is welded to portion 18 at a position spaced axially from the end part 19 of the shroud portion 16. At the inner end, the main sheet of the shroud portion 17 is bent radially at 24 to abut a radial face of inner component 15a and is then further bent axially away from the rotor at 25 to form an inner cylindrical part. Overlying the cylindrical part 25 is a second sheet of resilient metal 26 having a cylindrical central part. One end of the second sheet is bent radially at 27 to overlie a rotor side radial face of component 15a, which face is stepped back in a direction away from the rotor from the plane P. Thus, the inner rim 28 of the shroud section is gripped between parts 27 and 24.

The other end of the second sheet 26 is bent radially at 29 in the form of an annulus, the inner edge 30 of which just clears a flange 3'1 of the turbine axle 32. A slight clearance is maintained between component 15a and the hub 11 to allow controlled leakage of air between the edge 30 and the flange 31 into the radial turbine between component 15a and hub 1'1.

The other end of the cylindrical portion 18 of shroud component 16 is rigid with a flange portion 33 which is secured to the stationary part of the housing 13.

The method of constructing the shroud section and support means is illustrated more clearly by reference to FIGURE 3. The radially outer parts of the portions 16 and 17 are first welded together to grip the outer rim 2]. of the shroud section and the sheet of metal forming portions 29, 26 and 27 is inserted in place. At this point, the inner rim of portion 17 containing parts 24 and 25, is in the unstressed or equilibrium position illustrated in FIGURE 3, with a gap G of, for example, 0.020 inch between the part 24 and the adjacent radial face of component 15a. The gap G is closed by the application of an axial load, in the present embodiment, of about 145 pounds, in the direction shown by the arrows Q. While the parts are under load, the portions 25 and 26 are seam or stitch welded at 33. The inner rim 28 of the shroud section is drawn axially away from the rotor with respect to the outer rim 21 by the application of the axial load and remains held in this position by the weld at 33 after the axial load is removed so that the axial edge areas of the dividing surfaces of the components 15a, 15b, 150 are pressed against one another and securely sealed. At the same time, due to the resilient construction of the support means, a certain amount of radial displacement of the components is allowed, to compensate for the stresses which occur due to the thermal gradients set up in the shroud.

Since the temperature and radial thermal gradient to which the shroud is subjected is the greatest at the periphery, that is, near the input of the turbine, the outermost of the concentric components, 150, is given the smallest radial dimension, the radial dimension of succeeding components increasing towards the hub as the radial thermal gradient decreases. The components are strengthened by the provision of axially extending annular ribs, directed oppositely to the direction of the rotor, the central and outer components 15b and 15c having two such ribs separated by a radial planar portion. The ribs add to the strength of the sections, and in the case of components 15b and 15c, the dividing edge areas are formed in such ribs to give added strength to the joint.

It will be appreciated that many modifications may be made within the spirit and scope of the invention. For example, it is not necessary that the tension be applied in the opposite direction, provided that the overlapping was arranged in the opposite sense to that shown. The exact formation of the overlapping may be varied. For example, the overlapping may take the form of slot and groove joints or of oblique scarf joints, but the illustre-ted arrangement has been found to lead to a satisfactory seal with reasonable economy. The support means may be arranged in different ways so long as a differential axial tension is maintained between the inner and outer rims of the shroud section to maintain the components in sealing abutment.

Many further modifications may be made within the scope of the following claims. The rotor shown in the drawings is further described in our copendiug application Ser. No. 566,844 to A. B. Newland, and also in Ser. No. 585,013 to H. H. Langshur.

We claim:

1. In a centripetal turbine having:

stationary framewprk,

a rotor,

a rotor base,

a shroud including a section spaced from the rotor so as to cover at least the portion of said base exterior to the hub, and support means mounting said section to said framework,

the improvement wherein said shroud section comprises a plurality of separate concentric annular components arranged in mutual abutment to present a substantially continuous surface on the side adjacent said rotor,

said components having dividing edge areas which overlap in radial and axial directions so that when inner and outer rims of said section are under axial tension, the components are substantially rigidly interlocked and sealed against escape therebetween the high pressure gas from the rotor side, said support means being arranged to maintain such axial tension.

2. The improvement of claim 1 wherein each said component other than the innermost and outermost components has inner and outer edge areas comprising surfaces which face axially respectively in opposite directions so as to bear against the next adjacent respective components on opposite sides.

3. The improvement of claim 1 wherein said dividing edge areas at the radially outer extremities of said components overlie the dividing edge areas at the radially inner extremities of the next adjacent radially outward component on the side adjacent the rotor, the said inner rim of the section being held by said support means in tension, with respect to said outer rim, in a direction axially away from the rotor.

4. The improvement of claim 3 wherein said continuous surface lies in a radial plane and said edge areas are stepped so as to comprise faces which abut radially and faces which abut axially.

5. The improvement of claim 4 wherein each said component comprises at least one annular rib projecting axially in the direction away from said rotor.

6. The improvement of claim 5 wherein at least some of said components comprise a pair of said ribs separated by a radial planar portion.

7. The improvement of claim 1 wherein said shroud section support means comprises:

a cylindrical portion shaped at one end to engage and grip said outer rim of said section, and extending in a direction axially away from said rotor to an opposite end which is fixed to part of said stationary framework,

a tapering annular portion extending from an outer rim rigid with said cylindrical portion at a position spaced from said one end thereof, to an inner rim shaped to engage and grip said inner rim of said section, said inner rim of said tapering portion being in its engaged position resiliently displaced axially from its position of equilibrium so as to maintain said axial tension between the inner end and outer rims of the section.

8. The improvement of claim 7 wherein said dividing edge areas at the radially outer extremities of said components overlie the dividing edge areas at the radially inner extremities of the next adjacent radially outward component, on the side adjacent the rotor, the said inner rim of the section being held by said support means in tension, with respect to said outer rim, in a direction axially away from the rotor.

9. The improvement of claim 8 wherein said inner rim of said tapering portion is formed from two sheets of metal, a first sheet including the taper having a first rim part bent radially inwardly from the cone and adapted to abut a radial edge face of the innermost said component, and a second rim part bent from said first part axially away from the rotor, and

a section sheet having a cylindrical part inwardly overlying said second rim part of said first sheet and an edge part bent radially outwardly from the cylindrical part and overlying the extremity and part of a rotorside face of said innermost component,

the said axial part of the first sheet having an equilibrium position spaced from said innermost component and said second rim part of the first sheet being secured to said cylindrical part of said second sheet at a position displaced axially towards the rotor from said equilibrium position.

10. The improvement of claim 9 wherein said shaped one end of said cylindrical portion of the shroud section is formed from two sheets,

a first sheet including the cylinder and a rim part bent radially inwardly so as to abut a radial face of the outermost component, and

said second sheet having a cylindrical part overlying and secured to said cylinder of said first sheet and a rim part bent radially inwardly from said cylindrical part and overlying the extremity and part of a rotor-side face of said outermost component.

11. The improvement of claim 10 wherein the said rotor-side edge faces engaged by the support means are stepped back from the plane of the remainder of the continuous rotor-side surface of the shroud section.

12. The improvement of claim 1 wherein the components are of successively increasing radial dimension from the outer periphery to the inner periphery.

13. The improvement of claim 12 wherein there are three concentric components.

14. The improvement of claim 10 wherein said tapering portion tapers frusto-conically.

No references cited.

EVERETT A. POWELL, JR., Primary Examiner. 

1. IN A CENTRIPETAL TURBINE HAVING: STATIONARY FRAMEWORK A ROTOR, A ROTOR BASE, A SHROUD INCLUDING A SECTION SPACED FROM THE ROTOR SO AS TO COVER AT LEAST THE PORTION OF SAID BASE EXTERIOR TO THE HUB, AND SUPPORT MEANS MOUNTING SAID SECTION TO SAID FRAMEWORK, THE IMPROVEMENT WHEREIN SAID SHROUD SECTION COMPRISES A PLURALITY OF SEPARATE CONCENTRIC ANNULAR COMPONENTS ARRANGED IN MUTUAL ABUTMENT TO PRESENT A SUBSTANTIALLY CONTINUOUS SURFACE ON THE SIDE ADJACENT SAID ROTOR, SAID COMPONENTS HAVING DIVIDING EDGE AREAS WHICH OVERLAP IN RADIAL AND AXIAL DIRECTIONS SO THAT WHEN INNER AND OUTER RIMS OF SAID SECTION ARE UNDER AXIAL TENSION, THE COMPONENTS ARE SUBSTANTIALLY RIGIDLY INTERLOCKED AND SEALED AGAINST ESCAPE THEREBETWEEN THE HIGH PRESSURE GAS FROM THE ROTOR SIDE, SAID SUPPORT MEANS BEING ARRANGED TO MAINTAIN SUCH AXIAL TENSION. 